count_div_test.rb

# test cases that i've used for the lesson below:
# https://app.codility.com/programmers/lessons/5-prefix_sums/count_div/

require 'minitest/autorun'

class CountDivTest < Minitest::Test
  def test_solution
    a, b, k = [6, 11, 2]
    assert_equal 3, solution(a, b, k)

    a, b, k = [7, 11, 2]
    assert_equal 2, solution(a, b, k)

    a, b, k = [6, 11, 3]
    assert_equal 2, solution(a, b, k)

    a, b, k = [7, 11, 3]
    assert_equal 1, solution(a, b, k)
  end

  def test_minimal
    a, b, k = [0, 0, 11]
    assert_equal 1, solution(a, b, k)
  end

  def test_k_larger_than_b
    a, b, k = [12, 15, 20]
    assert_equal 0, solution(a, b, k)
  end

  def test_k_smaller_than_b
    a, b, k = [12, 27, 20]
    assert_equal 1, solution(a, b, k)
  end

  def test_extreme_ifempty
    a, b, k = [10, 10, 5]
    assert_equal 1, solution(a, b, k)

    a, b, k = [10, 10, 7]
    assert_equal 0, solution(a, b, k)

    a, b, k = [10, 10, 20]
    assert_equal 0, solution(a, b, k)
  end

  def test_medium_numbers
    a, b, k = [100, 900, 32]

    count = 0
    100.upto(900) do |i|
      count += 1 if i % k == 0
    end

    assert_equal count, solution(a, b, k)
  end

  def test_large_input
    a, b, k = [101, 123_456_789, 10_000]
    assert_equal 12345, solution(a, b, k)

    a, b, k = [0, 2_000_000_000, 1]
    assert_equal 2_000_000_001, solution(a, b, k)
  end

  def test_large_k
    a, b, k = [0, 1_999_999_999, 2_000_000_000]
    assert_equal 1, solution(a, b, k)

    a, b, k = [1, 1_999_999_999, 2_000_000_000]
    assert_equal 0, solution(a, b, k)
  end
end